Prevention of Exotic Species Introductions to the San Francisco Bay Estuary: A Total Maximum Daily Load Report to U.S. EPA

California Regional Water Quality Control Board, San Francisco Bay Region

Executive Summary Background Exotic species are one of the greatest threats to the integrity of the San Francisco Estuary ecosystem, perhaps as great as any pollutant regulated under the Clean Water Act (CWA), and currently they continue to be discharged into the estuary, primarily in ships’ ballast water. Ongoing introductions of exotic species, including pathogens, to the San Francisco Estuary threaten the ecology, economy, and public health of the San Francisco Bay Region. Treating exotic species as pollutants is consistent with the existing regulatory framework of the CWA. One of the principles of water quality control is biological control. EPA regulates biological pollutants such as pathogens under various programs of the CWA. Exotic species meet the definition of “pollutant” at Section 502 of the CWA, for the reason that they are “biological materials…discharged into water,” and they impair or threaten to impair the full range of designated beneficial uses of waterbodies in the San Francisco Estuary. An exotic species is defined as any species that is not native to a particular ecosystem, including its seeds, eggs, spores, or other biological material capable of propagating that species. Synonyms for exotic species include non-native species, nonindigenous species, and alien species. Problem Statement When an exotic species is introduced into a new ecosystem, there is potential for significant disruption of the balance among existing native and naturalized species, especially if the exotic species competes with native species for resources, preys on native species, and/or no predators are able to control the population of the exotic species. When an exotic species does or is likely to cause economic or environmental harm, or harm to human health, it is known as an “invasive species.” Yet another synonym for such an organism occurring in or near waters is “aquatic nuisance species1 ,” or ANS, as defined in the National Invasive Species Act (NISA). Competition with and predation by invasive species affects 49 percent of endangered or threatened species in the U.S. (Wilcove et al., 1998). About 42 percent of the species listed as endangered or threatened under the Endangered Species Act of 1973 are at risk primarily because of exotic species. Controlling the impacts of exotic species already introduced, is costing Americans in excess of $123 billion per year, mostly from agricultural pests, but the costs of ANS have topped $5 billion per year and are rising (Pimentel et al., 1999).